Generally, each piece used in clockwork movements includes an arbor provided at both of its ends with pivots, each engaged in a bearing. Pivot organs made up of a bearing and a pivot are traditionally used to ensure axial and radial positioning of the rotating pieces present in the movements.
The pivot is generally made of steel and the bearing is for example made of brass, bronze or ruby, the pairs of materials being chosen such that the frictional torque between the bearing and the pivot is as small and consistent as possible. Thus, according to patent U.S. Pat. No. 2,546,002, it is known to make bearings from precious stones such as diamond or sapphire.
However, the pivot members made from these pairs of materials are still not fully satisfactory regarding the value of the frictional torque obtained. They require lubrication using oil that tends to deteriorate with time.
To try to resolve this problem, patent FR 1 033 071 proposes to modify the shape of the pivots and stones by using a stone having a hole with a circular cross-section and a steel pivot, having, at its surface opposite the stone, a polygonal-shaped cross-section, so as to reduce the contact surfaces between the pivot and the stone. However, this solution is not satisfactory because it still requires lubrication, an oil-sink being provided at the stone.
One aim of the present invention is therefore to offset this drawback, by proposing a pivot organ that makes it possible to further decrease the frictional torque between the bearing and the pivot so as not to require lubrication without, however, affecting wear.
Another aim of the present invention is to propose a pivot organ whereof the elements can be easily manufactured.